Alkaline zinc electroplating bath

ABSTRACT

The alkaline zinc electroplating bath of the present invention contains as brightening agent the reaction product of A. POLYETHYLENE IMINE OR POLYPROPYLENE IMINE WITH B. AN AROMATIC ALDEHYDE, C. AMMONIA AND/OR ETHYLENEDIAMINE, OR DIETHYLENE TRIAMINE AND D. EPICHLOROHYDRIN. Due to the addition of said reaction product its cyanide content can be considerably reduced without impairing the brightness of the zinc deposit.

United States Patent Koch Oct. 28, 1975 [54] ALKALINE ZINCELECTROPLATING BATH 3,472,743 10/1969 Rushmere 204/55 Y 3,655,534 4/1972Kampe [76] Inventor Remha'd Koch 6081 Gemshem" 3,806,431 4/1974 Koch204/55 Y Germany [22] Filed: Nov. 14, 1973 Primary Examiner-G. L. Kaplan[2U Appl No 415,757 Attorney, Agent, or FirmErich M. H. Radde [301Foreign Application Priority Data [57] ABSTRACT Nov. 15, 1972 Germany2256000 The alkaline Zine electroplating bath of the Pleserlt ventioncontains as brightening agent the reaction 52 us. c1. 204 55 Y; 260/292EP; 260/72 R product of [51] Int. C1. C25D 3/24 P y y mine or P yp pymine with 58 Field of Search 204/55 Y, 55 R, 432, 44 an aromaticaldehyde.

c. ammonia and/or ethylenediamine, or diethylene References Citedtriamine and UNiTED STATES PATENTS eplchlmhydm- 2288318 6/1942 Hoffman204,55 Y Due to the addition of said reaction product its 2,630,7126/1954 Diggin et a1 204,55 Y cyanide content can be considerably reducedwithout 2,791,554 5 1957 Winters 204/55 Y impairing the g ne f h zin p i2,860,089 11/1958 Jackson 204/55 Y 3,227,638 1/1966 Burnson 204/55 Y x 9Clams, N0 Drawmgs ALKALINE ZINC ELECTROPLATING BATH BACKGROUND OF THEINVENTION 1. Field of the Invention bath and more particularly to a Thepresent invention relates to a cyanide-containing zinc electroplatingbath cyanide-containing zinc electroplating bath yielding smooth andbright to fully bright zinc plates, to a process of producing saidbaths, and to a method of using such baths for electroplating.

2. Description of the Prior Art Cyanide-containing zinc baths forelectrolytic deposition of zinc plates are known. Bright zinc plates ofexcellent throwing power, metal distribution, and brilliance areproduced, when using such baths.

Cyanide-containing Zinc baths require the addition of specialbrightening additives in order to produce zinc layers of highbrilliance. Such additives are, for instance, amino-aldehyde derivativessuch as aldehydealkanolamines, water-soluble polyvinyl alcohols, saltsof metals of the groups VIIB or VIII of the Periodic System, and sugars.The amounts of such additives, however, must be carefully adjusted inrelation to the zinc content and/or the cyanide content of the bath.

More recently, and in ever increasing numbers, weakly acid or alkalinecyanide-free zinc baths or baths of a low cyanide content are used inorder to meet the requirements of pollution control which demandsspecial waste disposal treatment and equipment so as to conform withlegal provisions. However such cyanidefree zinc baths or baths of a lowcyanide content usually do not yield zinc coating of a brilliancecomparable to that attained with cyanide-containing zinc baths.

SUMMARY OF THE INVENTION It is one object of the present invention toprovide a novel and advantageous cyanide-containing zinc bath andespecially a zinc bath of a low cyanide content which yields bright zinccoatings, has a satisfactory throwing power, and achieves good metaldistribution, said bath exhibiting the properties of a good zinc bath ofthe usual high cyanide content, said bath permitting to considerablydecrease its cyanide content even when operating at a current densitybelow I amp./sq.dm.

Another object of the present invention is to provide a simple andeffective process of producing such a zinc bath.

A further object of the present invention is to use such a zinc bath forzinc electroplating and the deposition of a bright zinc coating.

Other objects of the present invention and advantageous features thereofwill become apparent as the description proceeds.

In principle the bright zinc plating bath according to the presentinvention contains, in addition to an alkali metal hydroxide, cyanideand zinc as suitable, salts to form zincate and complex zinc cyanideions, polyvinylalcohol or acetyl derivatives thereof, and if desired,salts of metals of the Groups VII B and VIII of the Periodic System, anda monosaccharide or polysaccharide, as they are present in the knownbright zinc electroplating baths, a reaction product of a. apolyalkylene imine such as polyethylene imine or polypropylene iminewith b. an aromatic aldehyde, c. ammonia and/or ethylenediamine anddiethylene triamine respectively, and

d. epichlorohydrin. Said reaction product is prepared by first reactingcomponentsta) and (b) in an aqueous medium, such as water at atemperature between 20C. and 50C., adding component (c) andsubsequentlyadding component (d) and heating the reaction mixture to atemperature of between 30C. and 60C., if desired, with further dilutionof the reaction mixture with water. The solution of the reaction productobtained may be used without separating the reaction product. Theamounts of said reaction product (calculated as non-aqueous product)added to the zinc plating bath are between 0.1 g./l. and 10 g./l.,preferably between 0.2 g./l. and 5.0 g./l. of zinc bath. The amounts ofzinc are normally between 5 g./l. and 50 g./l. and the amounts ofcyanide are between 5 g./l. and g./l. of zinc bath. Such a bath has analkali metal cyanide: Zinc ratio (M-factor) between 1 and 3.2.

As aromatic aldehydes, there are preferably used benzaldehydes,halogenor hydroxyl-substituted benzaldehydes such as2,4-dichlorobenzaldehyde, phydroxy benzaldehyde, and other aldehydes ofthe general formula CHO In said formula R indicates hydroxyl and/orlower alkoxy with l to 4 carbon atoms and especially methoxy, while Xindicates one of the numerals 0, l, or 2. Preferred aldehydes of thistype are salicylaldehyde, anisaldehyde, vanillin, and veratraldehyde.The molecular proportions of the components of the brightening reactionproduct added to the zinc plating bath are preferably as follows: 7

Molecular proportion of polyethylene imine or respectively,polypropylene imine to aromatic aldehyde between about 1:: l and l 15;

molecular proportion of polyethylene imine or, re-

spectively, polypropylene imine to epichlorohydrin between about 1 3 andabout 1 40;

molecular proportion of ammonia or, respectively,

ethylene diamine or diethylene triamine to epichlorohydrin I l.

Salts of manganese or nickel are preferably used as salts of a metal ofthe Groups VIIB or VIII of the Periodic System. They are employed inamounts between 0.01 g./l. and 0.1 g./l. and preferably between 0.01g./l. and 0.05 g./l.

Polyvinylalcohol or an acetyl derivative thereof having a degree ofpolymerisation between about 300 and about 1500, such as sold under thetradename Mowiol by Farbwerke I-Ioechst is added in an amount between0.05 g./l. and 0.5. g./l. and preferably in an amount between 0.l g./l.and 0.5 g./l.

As monoand polysaccharides one or several of dextrose, glucose,saccharose and dextrines are preferably added in an amount between 0.01g./l. and 0.08 g./l.

"DESCRIPTION or THE PREFERRED EMBODIMENTS EXAMPLE 1 Smooth and even,bright zinc deposits on iron are obtained with a bath of the followingcomposition, said bath having excellent throwing power, metaldestribution, and brilliance. The amounts of its components are given asamounts in grams per liter of bath:

Zinc calculated as zinc oxide Sodium cyanide Sodium hydroxide Reactionproduct of a. polyethylene imine, b. veratraldehyde, c. ammonia, and d.epichlorohydrin in the following proportions:

(a) (b) l:l moles; (a) I (d) 1:3 moles; (C) (d)= 1:] molesPolyvinylalcohol (Mowiol N 30-88) Dextrose Manganese sulfate Nickelsulfate 0.2 g. to 5.0 g. 0.05 g. to 0.5 g. 0.5 g. to 5.0 g.

Such a bath is used at a bath temperature between C. and 35C.

The current density is between 0.3 amp./sq.dm. and 5.0 Amp./sq./dm.

EXAMPLE 2 Smooth and even, bright zinc coatings on iron are producedwith the following bath having an excellent throwing power, metalinhibition, and brilliance. The amounts of the components are calculatedas amounts in grams per liter of bath:

7 g. to g. 81.5 g. 95 g.

Zinc (calculated as zinc oxide) Sodium cyanide.

Sodium hydroxide.

Reaction product made from g 0.05 g. to 0.5 g.

Such a bath is used at a bath temperature between 15C. and C.

The current density is between 0.3 Amp./sq.dm and 5.0 Amp/sq. dm.

EXAMPLE 3 The reaction product of the polyalkylene imine, an aromaticaldehyde, ethylene diamine and/or ammonia, and epichlorohydrin isprepared as follows:

25 g. (0.01 mole) of polyethylene imine are reacted with 53 g. (0.5mole) of benzaldehyde with the addition of 50 cc. of water at atemperature of 50C. within about 30 minutes. The reaction mixture iscooled to room temperature. 24 g. (0.4 mole) of ethylene diamine areadded thereto and the resulting mixture is made up with water to 300 cc.Thereafter, there are added portion by portion 2.76 g. to 27.6 g. (0.03mole to 0.3 mole) and subsequently 36.8 g. (0.4 mole) of epichlorohydrinin such a manner that the reaction temperature does not exceed atemperature of 60C. The reaction mixture is then made up with water toone liter.

Polyethylene imine can be replaced in said example by the equivalentamount of polypropylene imine.

In place of ethylene diamine, there can also be used 40 cc. of a 36%ammonia solution.

The benzaldehyde can be replaced by equimolecular amounts of otheraromatic aldehydes.

I claim:

1. In an alkaline zinc electroplating bath comprising, in aqueoussolution, a zinc salt, an alkali metal cyanide, an alkali metalhydroxide, and a water-soluble polyvinylalcohol, the improvement whichcomprises said bath containing, as brightening agent, between about 0.1g./l. and about 10.0 g./l. of the reaction product obtained by reactingin an aqueous medium at a temperature between about 20 and 50C.

a. a polyalkylene imine selected from the group consisting ofpolyethylene imine and polypropylene imine, with b. an aromaticaldehyde, in a molar ratio between about 1:1 to 1:50 of imine toaldehyde, adding c. a basic agent selected from the group consisting ofammonia, ethylene diamine, and diethylene triam' ine, and

d. epichlorohydrin, in a molar ratio between about 1:3 to 1:40 of imineto epichlorohydrin and about 1:1 of basic agent to epichlorohydrin, andheating the reaction mixture.

2. The zinc electroplating bath of claim 1 additionally containing asalt of a metal selected from the group consisting of a metal of theGroups VllB and VIII of the Periodic System.

3. The alkaline zinc electroplating bath of claim 2, wherein said metalsalt is present in an amount of between about 0.01 and 0.1 g./l.

4. The zinc electroplating bath of claim 1 additionally containing amonoor polysaccharide.

5. The alkaline zinc electroplating bath of claim 3, wherein said monoorpoly-saccharide is present in an amount of between about 0.01 and 0.08g./l.

6. The zinc electroplating bath of claim 1 additionally containing asalt of a metal selected from the group consisting of a metal of thegroups VllB and VIII of the Periodic System and a monoor polysaccharide.

7. The alkaline zinc electroplating bath of claim 6, wherein said metalsalt is present in an amount of between about 0.01 and 0.1 g./l. andsaid monoor polysaccharide is present in an amount between about 0.01and 0.08 g./l.

8. The zinc electroplating bath of claim 1, in which the aromaticaldehyde component of the reaction product is an aromatic aldehydeselected from the group consisting of benzaldehyde, ahalogen-substituted benzaldehyde, a hydroxyl-substituted benzaldehyde,atoms and and an aromatic aldehyde of the formula X is a numeralselected from the numerals of 0, l,

and 2. 9. The alkaline zinc electroplating bath of claim 1, in CH whichsaid bath contains, as brightening agent, between about 0.2 g./l. andabout 5.0 g./l of the reaction product X Of a. a polyalkylene imineselected from the group consisting of polyethylene imine andpolypropylene 1O imine, with b. an aromatic aldehyde,

- c. a basic agent selected from the group consisting of in whichammonia, ethylene diamine, and diethylene triam- R is a member selectedfrom the group consisting of ine, and

hydroxyl and lower alkoxy with l to 4 carbon d. epichlorohydrin.

UNITED STATES PATENT OFFICE CERTIFHIATE OF CQHRECTION Patent No.3,915,815 Dated October 28, 1975 Inventor) REINHARD KOCH It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 1, line 6: "bath and more particularly" should be cancelled.

Q line 7: "to a" should be cancelled.

line 8: After "bath" there should be added and more particularly to aSigned and Sealed this tenth Day Of February 1976 [SEAL] Arrest:

RUTH C. MA SON C. MARSHALL DANN Allemn g Officer Commissioner oj'Parentsand Trademarks

1. IN AN ALKALINE ZINC ELECTROPLATING BATH COMPRISING, IN AQUEOUSSOLUTION, A ZINC SALT, AN ALKALI METAL CYANIDE, AN ALKALI METALHYDROXIDE, AND A WATER-SOLUBLE POLYVINYLALCOHOL, THE IMPROVEMENT WHICHCOMPRISES SAID BATH CONTAINING, AS BTIGHTENING AGENT, BETWEEN ABOUT 0.1G./1. AND ABOUT 10.0 G/1. OF THE REACTION PRODUCT OBTAINED BY REACTINGIN AN AQUEOUS MEDIUM AT A TEMPERATURE BETWEEN ABOUT 20* AND 50*C. A. APOLYALKYLENE IMINE SELECTED FROM THE GROUP CONSISTING OF POLYETHYLENEIMINE AND POLUPROPYLENE IMINE, WITH B. AN AROMATIC ALDEHYDE, IN A MOLARRATIO BETWEEN ABOUT 1:1 TO 1:50 OF IMINE TO ALDEHYDE, ADDING C. A BASICAGENT SELECTED FROM THE GROUP CONSISTING OF AMMONIA, ETHYLENE DIAMINE,AND DIETHYLENE TRIAMINE, AND D. EPICHLOROHYDRIN, IN A MOLAR RATIOBETWEEN ABOUT 1:3 TO 1:40 OF IMINE TO EPICHLOROHYDRIN AND ABOUT 1:1 OFBASIC AGENT TO EPICHLOROHYDRIN, AND HEATING THE REACTION MIXTURE.
 2. Thezinc electroplating bath of claim 1 additionally containing a salt of ametal selected from the group consisting of a metal of the Groups VIIBand VIII of the Periodic System.
 3. The alkaline zinc electropLatingbath of claim 2, wherein said metal salt is present in an amount ofbetween about 0.01 and 0.1 g./l.
 4. The zinc electroplating bath ofclaim 1 additionally containing a mono- or polysaccharide.
 5. Thealkaline zinc electroplating bath of claim 3, wherein said mono- orpoly-saccharide is present in an amount of between about 0.01 and 0.08g./l.
 6. THE ZINC ELECTROPLATING BATH OF CLAIM 1 ADDITIONALLY CONTAININGA SALT OF A METAL SELECTED FROM THE GROUP CONSISTING OF A METAL OF THEGROUPS VIIB AND VIII OD THE PERIODIC SYSTEM AND A MONO-ORPOLYSACCHARIDE.
 7. The alkaline zinc electroplating bath of claim 6,wherein said metal salt is present in an amount of between about 0.01and 0.1 g./l. and said mono- or poly-saccharide is present in an amountbetween about 0.01 and 0.08 g./l.
 8. The zinc electroplating bath ofclaim 1, in which the aromatic aldehyde component of the reactionproduct is an aromatic aldehyde selected from the group consisting ofbenzaldehyde, a halogen-substituted benzaldehyde, a hydroxyl-substitutedbenzaldehyde, and an aromatic aldehyde of the formula
 9. The alkalinezinc electroplating bath of claim 1, in which said bath contains, asbrightening agent, between about 0.2 g./l. and about 5.0 g./l of thereaction product of a. a polyalkylene imine selected from the groupconsisting of polyethylene imine and polypropylene imine, with b. anaromatic aldehyde, c. a basic agent selected from the group consistingof ammonia, ethylene diamine, and diethylene triamine, and d.epichlorohydrin.